Many communication systems have elements or subs-systems that introduce undesirable nonlinear distortions into signals they transmit. For example, radio signal transmitters of wireless communication signals typically include power amplifiers (PA) at the output thereof, which often have non-linear input-output characteristics, and therefore introduce non-linear distortions into the output wireless signal. Linearization of a PA has been a challenging problem, especially for multi-carrier communication systems. A key issue in such linearization is to characterize the nonlinear-distortion of the multi-carrier signal caused by the PA nonlinearity. Once the effect of the PA nonlinearity on the signal is suitably characterized, the signal entering the PA can be pre-distorted in such a way that pre-compensates for the PA nonlinearity, reducing the nonlinear distortion of the output signal to a suitably low level.
U.S. Pat. No. 6,885,241, which has common inventors with the present application and is assigned to the assignee of the present application, discloses a type-based approach to generating a based-band pre-distortion function for pre-compensating single-frequency signals prior to entering the PA. Although the method disclosed in the U.S. Pat. No. 6,885,241 can be configured for use with multi-frequency signals wherein the number of multiplexed frequency channels is small, it does not provide a good estimation of the required phase compensation when the signal contain a large number of asynchronous multiplexed carriers.
An object of the present invention is to provide a method and circuit for compensating for nonlinear distortions of frequency-multiplexed signals in multi-carrier communication systems.